The invention concerns a process and apparatus for decorating an article, more particularly on the basis of a program containing digitised image information.
It will be noted at this juncture that when reference is made to decorating an article or to decoration, that term is not to be interpreted in a limiting sense. On the contrary the term decorate, decoration and so forth is to be interpreted in its broadest sense, for example in such a way as also to embrace not just images but any other graphics, description, other text, digits, numbers and the like. Similarly the term article is intended to embrace any form of article to which the process and apparatus according to the invention can be applied, one such example thereof being a CD, as well as credit cards, telephone cards and the like.
Nowadays the procedure for printing on individual articles such as CDs, credit cards, telephone cards and similar articles is implemented without exception with the use of processes in which the printing inks are applied to the article to be decorated by means of at least one transfer element and the transfer element is of a configuration corresponding to the print image to be transferred or is provided with the print image to be transferred. The former case can involve for example the use of a screen printing arrangement in which the printing ink is applied to the article by means of a squeegee or doctor, through a stencil which is provided with the print image. The second case frequently involves the use of the offset printing process in which the printing ink corresponding to the print image to be produced is firstly applied to the printing blanket on a cylinder and from there to the article.
A common aspect of all those processes which, for transfer of the ink on to the article to be printed, require contact between the article and the transfer means, is that the printing mechanisms must be of such a configuration as to correspond to the print image to be produced on the article, that is to say for example they must be provided with print blocks or plates or stencils of a suitable configuration. The consequence of this is that, upon a change in the articles to be printed upon and thus upon a change in the print image to be applied, the printing mechanism has to be appropriately converted, that is to say, it has to be fitted with a new screen printing stencil or a new plate cylinder. That conversion procedure can demand a considerable amount of time, during which production ceases, particularly when the apparatus has a plurality of printing mechanisms, as is the case for example when producing a multi-color print image. Furthermore, with the machines which are usually employed nowadays, the conversion procedure, which includes the necessary step of adjusting and setting the printing mechanisms to the print image of the respectively following batch of articles to be printed upon, requires operators of a very high level of skill and training if the machine is to produce a high-quality print image after conversion. The problems which arise in such a context can give rise to major disadvantages not least for the reason that in many cases, for example when dealing with CDs, telephone cards and credit cards, very small batch numbers frequently have to be printed upon. Batch sizes of only several hundreds of CDs or telephone cards are not uncommon. At the same time the demands made in terms of the quality of the print image are becoming greater and greater.
An object of the present invention is to provide a process for decorating an article, which makes it possible to produce high-quality print images, with a high production capacity, while at the same time apparatus conversion times can be so short that it is possible to economically decorate even very small batch numbers.
Another object of the present invention is to provide an apparatus which while being of a simple structure and involving a simple mode of operation can produce high-quality print images with a high rate of item production, together with a capability for rapid conversion from one printing mode to another.
Still another object of the present invention is to provide a process for printing on an article, which affords an enhanced degree of adaptability to varying operating and production requirements.
In accordance with the principles of the present invention, in a first aspect of the process, the foregoing and other objects are attained by a process for decorating an article in which printing ink is applied from nozzles in dot form to the article which is carried by a holder, in dependence on a program which contains digitised image information, and individual ink dots go together to form at least a partial print image. The holder carrying the article to be printed upon is moved along a transport path through at least one print station provided with a print head having the nozzles which are controllable in dependence on the program. At least a part of the nozzles is actuated in accordance with the program during the transportation movement of the article, and the holder for the article is transported using a linear motor along the transportation path.
As will be seen in greater detail from the description hereinafter of preferred embodiments of the invention, this process in the first aspect of the invention can be considered as involving an inkjet process in combination with a program containing digital image information, for printing on individual objects, and makes it possible to produce print images, including multi-color images, of very high quality. It is also possible to achieve a high production rate. This is also to be attributed to the fact that printing on the article can take place during the transportation movement through the printing machine, which is necessary in any case. The use of a linear motor contributes considerably to achieving a good quality of print image as the linear motor permits accurate co-ordination of the speed of transportation movement and the printing operation in the respective print station.
Further in accordance with the principles of the present invention, in a second aspect of the process of the invention, the foregoing and other objects are attained by a process for decorating an article in which firstly in dependence on a program including digitised image information, a latent image which is formed by electrostatically charged regions on a dielectric surface of the article to be decorated and which corresponds to the decoration to be applied is produced by charge transfer, whereupon the surface is brought into contact with ink particles of opposite charge, in order thereby to produce a decoration corresponding to the latent charge pattern. The article is moved along a transportation path through at least one station provided with an ionographic print head which is controllable in dependence on the program and in which charge carriers are generated by means of electrodes. A stream of charge carriers of the desired polarity is transferred on to dielectric regions of the surface of the article to form a latent pattern. The holder for the article is transported using a linear motor along the transportation path.
As will be seen in greater detail hereinafter, in that procedure therefore the ionographic print head in which the charged particles are generated, which are then transferred in the form of an ion stream on to the dielectric surface to form the latent pattern, by virtue of the voltage drop between the print head or electrodes therein and the article to be decorated, is controlled in dependence on the digital image information-containing program. In this respect, as background information, attention is directed to U.S. Pat. No. 4,891,656, the disclosure of which is hereby incorporated hereinto as appropriate by virtue of reference thereto.
Further in accordance with the invention, in a first aspect of the apparatus, the foregoing and other objects are attained by an apparatus for decorating an article using a process in which printing ink is applied in dot form from nozzles to the article which is carried by a holder, in dependence on a program which includes digitised image information, with individual dots going together to form at least a partial print image. The apparatus includes at least one print station, at least one transportation path along which the article carried by the holder is transported through the at least one print station, with the at least one print station being provided with at least one print head which is controllable by the program and the individual nozzles of which are actuable by means of pulse control in accordance with the program. A linear motor is operative to transport the articles along the transportation path.
Further in accordance with the invention, in a second aspect of the apparatus, the foregoing and other objects are attained by an apparatus for decorating an article using a process in which a dielectric surface is provided, in dependence on a program containing digitised image information, with an electrostatic charge representing a latent pattern corresponding to the decoration to be applied, and is thereafter brought into contact with oppositely charged ink particles in order thereby to produce the decoration. The apparatus includes at least one transportation path along which the article to be decorated which is carried by a holder and which is provided with the dielectric surface is transported, and at least one station in which the electrostatic charge pattern is applied has at least one ionographic print head controllable by the program for producing charge carriers of the desired polarity. The print head has electrodes by which the charge carriers are generated and which are actuable in dependence on the program. The apparatus further includes a linear motor for transportation of the articles along the transportation path.
It will be seen therefore that in both aspects of the process and apparatus according to the invention, application of the decoration to an individual article is implemented in a contact-less manner so that, upon a change in the decoration or the print image to be applied, it is only necessary to change the program for controlling the respective print head or image-forming unit. It is also readily possible to change the program from one article to the following article, in which respect such a change can also be suitably programmed, so that for example there is the possibility of printing on for example credit cards with a uniform decoration, while however changing the card number and the name of the card holder from one card to the next. When making a change in the complete program, for example when changing over from one printing batch to another, it is sufficient for the operator to replace one program carrier by another so that sample prints, if necessary at all, are only required in a very low number, before the normal production run can be initiated.
As the movements of the article to be printed upon on the one hand and the execution of the print program in the respective print station on the other hand must be synchronised, a preferred feature of the invention provides operating in such a way that the transportation movement of the article or the holder carrying same is controlled in dependence on the execution of the program, as this generally permits a greater degree of flexibility in regard to the configuration of the program, for example in such a way that the movement of the article during the printing operation can be decelerated or accelerated or the article can be brought to a halt so that it is possible to apply to a specific small region, more ink in the form of a plurality of successive ink droplets or more densely disposed charge points.
It is however also possible to operate in such a way that for example the article is transported through the process and apparatus at a constant speed and the program in the print station is called up in dependence on the movement of the article.
The holder for the article can be carried by the primary portion of the linear motor. That affords the advantage that, when there are a plurality of holders and thus a plurality of transportation carriages, for simultaneous treatment of a plurality of articles in the printing machine, the movements of the individual transportation carriages can be controlled independently of each other, without involving a high level of complication and expenditure. The independent control of the movement of the carriages may be of significance for the reason that, particularly in the case of multi-color printing machines, the articles and thus also the holders carrying them pass through a plurality of stations in the machine and different speeds, residence times and the like may be required in the individual stations. The option of mutually independently controlling the individual holders or the carriages carrying same, in regard to the movements thereof, can contribute to achieving a high production capacity. It will be appreciated however that the converse arrangement in which the holder is carried by the secondary portion of the linear motor is also a possible option. It will be noted however that this may involve a markedly higher level of structural and circuitry complication and expenditure if the individual carriages are to be controllable independently of each other in regard to their movements. The movements of the individual carriages outside the at least one print station and any further treatment stations that may be involved can also be controlled in dependence on a program.
Further objects, features and advantages of the invention will be apparent from the description hereinafter of preferred embodiments of the invention.